The present invention relates in general to a heat treating apparatus using microwaves for continuously treating a substance containing nuclear materials with consideration of the criticality safety of the nuclear materials, and more particularly to a heat treating apparatus using microwaves for continuously heat treating a solution and/or slurry containing nuclear materials such as plutonium, uranium and so forth, in nuclear fuel production facilities or spent fuel reprocessing facilities. The term "heat treating" is used herein with its generic meaning including various treatments effected by heating such as evaporation, drying, roasting, reduction, thermal denitrating and so forth, as well as various treatments conducted simultaneously with heating, such as mixing and crushing.
The nuclear fuel materials such as plutonium, uranium and so forth which are handled in nuclear fuel production facilities and recovered in spent fuel reprocessing facilities are generally in the form of a solution and, in some cases, in the form of a slurry. In a currently used method of thermally denitrating these substances, they are placed in a planar dish of a predetermined depth which is determined by taking the criticality safety thereof into consideration, and microwaves are applied directly to the substances. In the heat treatment using microwaves, the nuclear material, unlike when it is heated by steam or by electric devices, is heated directly, and it provides an improvement in the heating efficiency and allows the heating time to be minimized. This reduces the exposure to the nuclear materials and provides a uniform temperature distribution. As a result, a powder having excellent properties can be obtained. However, in the conventional heating system using microwaves as described above, the nuclear material which is treated by a batch process cannot be treated at a high rate, and it is impossible to continuously treat the material.
There have been several attempts at processing nuclear material at an increased rate, such as, for example, a method of simultaneously heating nuclear material placed in a plurality of suitably arranged dishes, and a supposed method of using an ordinary rotary kiln used in various conventional heat-treating methods. The former method requires a larger installation and facilities, and the latter does not provide a reliably high criticality safety. Therefore, it is difficult to employ these methods in practice.
Under the circumstances, there is a strong demand for the development of a compact heat treating apparatus of the type concerned, which has a higher processing rate and which is capable of controlling the criticality safety of the nuclear material.
The present invention has been developed in view of the actual conditions and circumstances of the prior art.